1. Field of the Invention
The present invention relates to a unit of buckle component members and a buckle.
2. Description of the Related Art
FIG. 7 shows a conventional buckle 110 as an example (see Japanese Patent Application Publication (JP-B) No. 2-4281).
In the buckle 110, a lock member guide 114 is mounted on a metal plate 112, and a lock member 116 is moved by the lock member guide 114 between a position where the lock member 116 is engaged with a tongue plate (hereinafter referred to as an engaging position) and a position where it is disengaged from the tongue plate (hereinafter referred to as an engagement-released position). Further, a pressing key 118 is mounted to the metal plate 112 in a slidable manner, and by sliding the pressing key 118, the lock member 116 is moved from the engaging position to the engagement-released position and locking is thereby released.
As shown in FIG. 8, the lock member guide 114 and the pressing key 118 are made integral by being joined together by portions 120 to be broken, before the lock member guide 114 and the pressing key 118 are mounted to the metal plate 112. When the pressing key 118 is slid with side walls 122 of the pressing key 118 being engaged with side edges of the metal plate 112, the lock member guide 114 abuts against the metal plate 112 during the sliding and the sliding is stopped. When the pressing key 118 is slid further, the portions 120 to be broken are sheared due to shearing force acting thereon, and the lock member guide 114 and the pressing key 118 are separated from each other.
However, in the above-described buckle 110, a minimum sectional area portion of the portion 120 to be broken (that is, the portion having the smallest sectional area in an arbitrary cross-section which is either at the portion 120 to be broken or the vicinity thereof) is made parallel to a direction in which the pressing key 118 slides. On the other hand, tensile stress acting on the portion 120 to be broken when the portion 120 is sheared acts obliquely to a direction in which the portion 120 is sheared (that is, the direction in which the pressing key 118 slides), and therefore, the sheared portion is formed along a direction perpendicular to the tensile stress so as to intersect the direction in which the pressing key 118 slides. For this reason, the portion 120 to be broken is not broken along the minimum sectional area portion and the sectional length of the portion which is actually broken becomes longer. Therefore, a breaking force greater than necessary, that is, a force for sliding the pressing key 118, becomes necessary. Further, when the broken portion and the minimum sectional area portion do not coincide with each other as described above, broken portions are formed in plural places and members disposed between the broken portions are sometimes separated from both of the lock member guide 114 and the pressing key 118 and fall off. In this case, it is necessary to remove, by suction or sweeping, the pieces which have fallen off, thereby resulting in an increase in the number of manufacturing processes.